Project Summary Despite the fact that suicide is recognized as a leading cause of death in children under 12, there are few studies of suicide in prepubescent children and only a handful of studies focusing on preschoolers. However from a developmental perspective, early childhood may be a critical period in which to study emergent suicidal thinking and behavior, given significant growth and changes in emotion regulation, as well as developing cognitive capacities that include an emerging understanding of death. The investigators on this application previously examined suicidal thoughts, plans, and attempts in a clinical sample (n = 390) of 3- to 7-year-old children presenting to our psychiatric partial hospitalization program. A semi-structured diagnostic interview (conducted with a primary caregiver) revealed that suicidal thinking and behavior was associated with older child age and with higher rates of concurrent depression, oppositional defiant disorder (ODD), and posttraumatic stress disorder (PTSD) in univariate analyses, with age and depression remaining as significant predictors in a multivariate logistic regression model. As further support for the high-risk nature of preschoolers with suicidality, we also found that suicidal thoughts/behaviors was the strongest prospective predictor of time to readmission in multivariate analysis. This application seeks to further our understanding of very early suicidal thoughts and behaviors, using an RDoC approach for the selection of constructs that we hypothesize to be most closely related to risk for suicidal behavior in this age group. Specifically, this application seeks to better characterize underlying RDoC Positive and Negative Valence Systems as well as Cognitive Systems relevant to suicidality in preschoolers, as they may be a precursor to suicidal behavior during both school age years and adolescence. In order to address these questions, we will recruit an equal number of youth, 4 to 7 years old, with (n = 45) and without (n = 45) parent-reported suicidal ideation or behavior from a pediatric partial hospitalization program. In addition, we will examine the role of parental history of suicidal behavior on their children?s suicidality to lay the groundwork for understanding biologic risk for suicidality at this young age in a future larger trial. Exploratory questions related to young children?s understanding of death will also be examined. The long-term goals of this research are to determine whether risk factors associated with suicidality in this very young sample help explicate the trajectory of suicidal ideation and behavior from preschool to school aged children to adolescents as well as to identify specific vulnerability factors that may inform preventative interventions. This research addresses NIMH Strategic Objective 2.2, to, ?identify clinically useful biomarkers and behavioral indicators that predict change across the trajectory of illness?. It also addresses NIMH/National Action Alliance for Suicide Prevention?s Prioritized Research Agenda for Suicide Prevention key question of why do people become suicidal, particularly the recommended short- term objective of identifying cognitive dysfunction associated with suicide risk.